[dexangeles]

it's called hemoglobin because of heme (pronounced heem)
it's a protein that contains heme

[jdurg]

The differences in spelling are just due to cultural localities.  It's like how cesium is spelled caesium in most european countries, color is splled colour, sulfur is spelled sulphur, etc. etc.  They are both correct.

[savoy7]

Yes that is true.  O- does not contain any Rhesus anitbodies which means that it does not matter if the receiver is Rh+ or Rh-.  Also, the O blood type does not cause any rejection reactions with any blood type.  So O- is indeed the universal donor.  

Let's see how this posting goes

Blood typing -
everything said sounds pretty good - a little added info

On the surface of cells are proteins that stick out of the membrane.  If these proteins are large enough to initiate an immune response, they are commonly called antigens.  Antibodies are quartenary proteins that have a region that can attach to specific antigens.  Note:  these antibodies are specific to the antigen in most cases.

On human RBCs there are lots (LOTS) of antigens, A and B are two types (protein markers).  Therefore, a person with type A blood has the A antigen, B has the B antigen, AB has both and O is the absence of those two markers.

On to the whole donor part - - -
lets see if I can make a chart

type                 antigen                    antibodies               donate to                    receive from
A                          A                          against B                A & AB                             A & O
B                          B                          against A                B & AB                             B & O
AB                      A & B                         ----                      AB                                  AB,A,B,O
O                         ----                          A&B                      A,B,AB,O                         O

Hopefully the little chart kind of stays together - on a small scale transfusion - O is an universal donor and AB is the universal receiver.  If I would give type A blood to a type B person, the A antibodies they have would stick to the A antigens on the transfused blood and clot it.  O type doesn't have the A & B antigens for antibodies to stick to, so they can "universally" donate.  AB type doesn't have any A or B antibodies, so they can "universally" receive.

don't worry O, in the US - types O and A are the most common

Now to the rhesus factor  - named after the rhesus monkey - found on their blood
If one is + they have the rhesus antigen on their blood and no antibodies
type rH -  has no antigen & ***** at first no antibodies ***** I'll come back to that.

so type rH + can receive from type rH + or rH -
type rH - can receive from rH - ****special part***** they can receive a small transfusion from a rH + person once
only once - once that rH- person is exposed to the rH+ antigen they start developing antibodies against it - it usually takes about 10-14 days.  The next time they are exposed to rH+ antigen, their body will mount an immune response immediately, clotting the blood.

Where this comes to play?  When a rH - mother is preg w/rH + child.  The first time, there's no problem.  But, at birth the blood of the baby is mixed with that of the mothers.  Whamo - next time she is exposed to the rH+ antigen she will mount an immune response.  If this happens when she is preg with a rH + fetus, her body will send antibodies across the placenta and abort the fetus.  We now have a drug that hospitals give mothers after the first birth that stops this from happening.

In this response, I use "universally" with "" because in large transfusions, more markers besides the A, B and rH are used to type blood.  That's why managing a blood bank can be difficult.  My hats off to them.

I hope this makes sense - after reading the quality of answers on this site, I wanted to answer this completely.